The following patent documents disclose an insulation type DC power conversion circuit (referred to as an insulation type DC/DC converter or an insulating converter), the primary side and the secondary side of which are insulated by an insulating transformer. The insulating converter is effective to suppress ground leakage of current.
Patent document 1: JP H07-298513A
Patent document 2: JP 2008-312382A
Patent document 3: JP 2009-33800A (US 2009/0034300A1)
Patent document 4: JP 4527616
In a battery charging system, in which a DC power supply apparatus may be used, a secondary battery may be charged from a power supply source such as a commercial power source. In case that the secondary battery is mounted in a mobile vehicle such as a four-wheel car, a motorcycle, a ship and an airplane, a circuit mounted in the mobile vehicle sometimes has a large stray capacitance. For example, in a case that a secondary battery is mounted in a vehicle such as a plug-in hybrid car, a capacitance between a high-voltage circuit mounted in the car and a chassis of the car is large. The capacitance includes a capacitance of a filter circuit and stray capacitances of other circuits. The power supplied from the commercial power line system may leak to the ground through the stray capacitances. If leakage of current increases, a ground-fault breaker provided between the commercial power line system and the DC power supply apparatus will operate to shut off the power supply. An insulating converter, which uses a switching circuit and an insulating transformer, is effective to prevent ground leakage of current. The switching circuit and the insulating converter however lowers efficiency of power conversion.